Today non-contact optical sensor technology is used in many areas of biological research to help perform increasingly sensitive and time-constrained assays. In one application, an optical interrogation system can be used to monitor changes in the refractive index or variations in the optical response/optical resonance of an optical biosensor as a biological substance is brought into a sensing region of the biosensor. The presence of the biological substance alters the optical resonance of the biosensor when it causes a bio-chemical interaction like material binding, adsorption etc. . . . It is this alteration of the optical resonance that enables one to use the biosensor to directly monitor a biological event in label-free assays. Examples of biosensors include surface plasmon resonance (SPR) sensors and waveguide grating coupler (WGC) sensors. A detailed discussion about the structure and function of the WGC sensor is provided in the following documents:                U.S. Pat. No. 4,815,843 entitled “Optical Sensor for Selective Detection of Substances and/or for the Detection of Refractive Index Changes in Gaseous, Liquid, Solid and Porous Samples”.        K. Tiefenthaler et al. “Integrated Optical Switches and Gas Sensors” Opt. Lett. 10, No. 4, April 1984, pp. 137-139.        Ph. M. Nellen, K Tiefenthaler, W. Lukosz, “Integrated Optical Input Grating Couplers as Biochemical Sensors” Sensors and Actuators, 15, 273 (1988).The contents of these documents are incorporated by reference herein.        
The optical interrogation system used today to interrogate the biosensor can take many forms, and two of the more general forms are briefly described next. In one case, the optical interrogation system delivers a single-wavelength, high-angular content optical beam to the biosensor, and the output beam received from the biosensor provides some information about the angular response of the biosensor. This type of optical interrogation system is commonly referred to as an angular interrogation system since angular detection is employed to locate a dominant angle in the output beam which is indicative of the particular optical response/optical resonance of the biosensor. In another case, the optical interrogation system delivers a collimated optical beam containing a range of wavelengths to the biosensor, the output beam received from the biosensor provides some information about the wavelength response of the biosensor. This type of optical interrogation system is commonly referred to as a spectral interrogation system since the spectrum of the output beam is analyzed to locate the resonant wavelength in the output beam which is indicative of the particular optical response/optical resonance of the biosensor.
These types of optical interrogation systems work relatively well but there is still a desire to try and design a new and improved optical interrogation system that can be used to interrogate a biosensor to determine if a biomolecular binding event (e.g., binding of a drug to a protein) or if some other event occurred on a surface of the biosensor. Accordingly, there has been and is a need for a new and improved optical interrogation system that can be used to interrogate a biosensor. This need and other needs have been addressed by the optical interrogation system and interrogation method of the present invention.